Method and Assembly For Determining The Temperature Of A Test Sensor

ABSTRACT

Methods and systems accurately determine an analyte concentration in a fluid sample. In an example embodiment, a receiving port receives a test sensor. The test sensor includes a fluid-receiving area for receiving a fluid sample. The fluid-receiving area contains a reagent that produces a measurable reaction with an analyte in the fluid sample. The test sensor has a test-sensor temperature and the reagent has a reagent temperature. A measurement system measures the reaction between the reagent and the analyte. A temperature-measuring system measures the test sensor temperature when the test sensor is received into the receiving port. A concentration of the analyte in the fluid sample is determined according to the measurement of the reaction and the measurement of the test sensor temperature. A diagnostic system determines an accuracy of the temperature-measuring system. The calculation of the analyte concentration may be adjusted according to the accuracy of temperature-measuring system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/184,928, filed Jun. 8, 2009, the contents of which areincorporated entirely herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to a method and assembly fordetermining an analyte concentration in a sample of body fluid collectedon a test sensor. Specifically, the present invention generally relatesto a method and assembly for measuring the temperature of the testsensor to determine the temperature of a reagent reacting with theanalyte and to achieve an accurate determination of the analyteconcentration based on the reaction with the reagent. More specifically,the present invention generally relates to techniques for implementingand calibrating a temperature-measuring system to obtain more accurateand reliable temperature measurements of the test sensor.

BACKGROUND OF THE INVENTION

The quantitative determination of analytes in body fluids is of greatimportance in the diagnoses and maintenance of certain physiologicalabnormalities. For example, lactate, cholesterol and bilirubin aremonitored in certain individuals. In particular, it is important thatindividuals with diabetes frequently check the glucose level in theirbody fluids to regulate the glucose intake in their diets. The resultsof such tests can be used to determine what, if any, insulin or othermedication needs to be administered. In one type of blood-glucosetesting system, test sensors are used to test a sample of blood.

A test sensor contains biosensing or reagent material that reacts with,for example, blood glucose. For example, the testing end of the sensormay be adapted to be placed into contact with the fluid being tested(e.g., blood) that has accumulated on a person's finger after the fingerhas been pricked. The fluid may be drawn into a capillary channel thatextends in the sensor from the testing end to the reagent material bycapillary action so that a sufficient amount of fluid to be tested isdrawn into the sensor. The tests are typically performed using a meterthat receives the test sensor into a test-sensor opening and appliesoptical or electrochemical testing methods.

The accuracy of such testing methods however may be affected by thetemperature of the test sensor. For example, the result of the chemicalreaction between blood glucose and a reagent on a test sensor may varyat different temperatures. To achieve an accurate reading, the actualmeasurement is corrected based on the actual sensor temperature, takenright before the reaction begins. The conventional way to measure thetest sensor temperature involves reading a resistive value from athermistor placed near the test-sensor opening. The thermistorresistance recalculates the chemical reaction result. This correctionmethod is based on an assumption that a sensor temperature is the sameas the thermistor temperature placed near the test-sensor opening. Inreality, however, the thermistor, which is typically located on aprinted circuit board, actually provides the temperature of the meter.Because the temperature of the meter can be very different from the testsensor temperature, the analyte measurement may be inaccurate.

SUMMARY OF THE INVENTION

Aspects of the present invention provide methods and assemblies formeasuring the temperature of a reagent on a test sensor used to collecta sample of body fluid. The reagent reacts with an analyte in the sampleof body fluid and the level of reaction may be measured to determine theconcentration of analyte in the sample. The level of reaction may beaffected by changes in temperature of the reagent. By determining atemperature for the reagent, aspects of the present invention accountfor the reagent's sensitivity to temperature and thus obtain a moreaccurate calculation of the concentration of analyte in the sample.Further aspects of the present invention provide techniques forimplementing and calibrating a temperature-measuring system to obtainmore accurate and reliable temperature measurements of the test sensor.

Accordingly, embodiments provide a device for determining an analyteconcentration in a fluid sample. A receiving port receives a testsensor. The test sensor includes a fluid-receiving area for receiving afluid sample. The fluid-receiving area contains a reagent that producesa measurable reaction with an analyte in the fluid sample. The testsensor has a test-sensor temperature and the reagent has a reagenttemperature. A measurement system measures the reaction between thereagent and the analyte. A temperature-measuring system measures thetest sensor temperature when the test sensor is received into thereceiving port. A concentration of the analyte in the fluid sample isdetermined according to the measurement of the reaction and themeasurement of the test sensor temperature. A diagnostic systemdetermines an accuracy of the temperature-measuring system.

In an example embodiment, the diagnostic system above includes areference object that achieves at least one reference temperature. Thetemperature-measuring system measures at least one test temperature forthe reference object when the reference object achieves the at least onereference temperature. The diagnostic system determines the accuracy ofthe temperature-measuring system by comparing the at least one testtemperature to the corresponding reference temperature. Furthermore, thedevice may be calibrated according to the accuracy of thetemperature-measuring system.

Embodiments also provide a method for testing a meter. The meterdetermines an analyte concentration in a fluid sample collected on atest sensor by measuring a reaction between the analyte and a reagent onthe test sensor. The meter includes a temperature-measuring system thatdetermines a test sensor temperature. The meter uses the test sensortemperature as a parameter in determining the analyte concentration. Themethod includes the step of changing a temperature of a reference objectto a specified reference temperature. The reference object is positionedin the meter for measurement by the temperature-measuring system. Themethod also includes the step of determining, with thetemperature-measuring system, a test temperature for the referenceobject when the reference object achieves the reference temperature.Furthermore, the method includes the step of determining an accuracy ofthe temperature-measuring system by comparing the test temperature tothe reference temperature.

These and other aspects of the present invention will become moreapparent from the following detailed description of the preferredembodiments of the present invention when viewed in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a general diagnostic system, including a test sensorand a meter according to aspects of the present invention.

FIG. 2 illustrates the embodiment of FIG. 1 with the test sensorinserted into the meter.

FIG. 3A illustrates a partial view of a meter according to aspects ofthe present invention.

FIG. 3B illustrates an enlarged transparent partial view of the meter ofFIG. 3A.

FIG. 3C illustrates an internal side view of the meter of FIG. 3A.

FIG. 3D illustrates yet another internal view of the meter of FIG. 3A.

FIG. 3E illustrates yet another internal view of the meter of FIG. 3A.

FIG. 3F illustrates a temperature-measuring system that may be employedwith the meter of FIG. 3A according to aspects of the present invention.

FIG. 3G illustrates an embodiment of the temperature-measuring system ofFIG. 3F.

FIG. 3H illustrates an example processing system for the meter of FIG.3A.

FIG. 4 illustrates an example of a diagnostic test for atemperature-sensing system according to aspects of the presentinvention.

FIG. 5 illustrates another example of a diagnostic test for atemperature-measuring system according to aspects of the presentinvention.

FIG. 6 illustrates a view of a calibration device that may be employedto conduct a diagnostic test of a temperature-measuring system accordingto aspects of the present invention.

FIG. 7 illustrates a temperature-measuring system that may be employedwith a meter according to aspects of the present invention.

FIG. 8 illustrates an example of an integrated temperature measurementmodule according to aspects of the present invention.

While the invention is susceptible to various modifications andalternative forms, specific embodiments are shown by way of example inthe drawings and are described in detail herein. It should beunderstood, however, that the invention is not intended to be limited tothe particular forms disclosed. Rather, the invention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

Referring to FIG. 1, a test system 10 with a test sensor 100 and a meter200 is illustrated. The test sensor 100 is configured to receive a fluidsample and in conjunction with the meter 200 help determine theconcentration of a substance, such as an analyte, in the sample.Non-limiting examples of an analyte type include glucose, variouslipids, microalbumin, hemoglobin and its derivatives, fructose, lactate,or bilirubin. Additional substances may also be tested using the methodsdescribed below. Non-limiting examples of a fluid sample include wholeblood serum, whole blood, blood serum, blood plasma, urine and otherbody fluids such as interstitial fluid as well as non-body samples.

As shown in FIG. 1, the test sensor 100 includes a body 105 having afluid-receiving area 110 for receiving a sample of body fluid. Forexample, a user may employ a lancet or a lancing device to pierce afinger or other area of the body to produce the blood sample at the skinsurface. The user then collects this blood sample by placing an opening107 of the test sensor 100 into contact with the sample. The bloodsample flows from the opening 107 to the fluid-receiving area 110 via acapillary channel 108. The fluid-receiving area 110 contains a reagent115 which reacts with the sample to indicate the concentration of ananalyte in the sample. The test sensor 100 also has a meter-contact area112 which is received by the meter 200 as described in detail furtherbelow.

The test sensor 100 may be an electrochemical test sensor, as is wellknown in the art. An electrochemical test sensor typically includes aplurality of electrodes and a fluid-receiving area that contains anenzyme. The fluid-receiving area includes a reagent for converting ananalyte of interest (e.g., glucose) in a fluid sample (e.g., blood) intoa chemical species that is electrochemically measurable, in terms of theelectrical current it produces, by the components of the electrodepattern.

Alternatively, the test sensor 100 may be an optical test sensor, as iswell known in the art. Optical test sensor systems may use techniquessuch as, for example, transmission spectroscopy, diffuse reflectance, orfluorescence spectroscopy for measuring the analyte concentration. Anindicator reagent system and an analyte in a sample of body fluid arereacted to produce a chromatic reaction, as the reaction between thereagent and analyte causes the sample to change color. The degree ofcolor change is indicative of the analyte concentration in the bodyfluid. The color change of the sample is evaluated to measure theabsorbance level of the transmitted light.

As further illustrated in FIG. 1, the meter 200 includes a body portion205 with a test sensor opening 210, which includes a connector forreceiving and/or holding a test sensor 100. The meter 200 also includesa measurement system 220 for measuring the concentration of analyte forthe sample in fluid-receiving area 110. For example, the measurementsystem 220 may include contacts for the electrodes to detect theelectrochemical reaction for an electrochemical test sensor.Alternatively, the measurement system 220 may include an opticaldetector to detect the chromatic reaction for an optical test sensor. Toprocess information from the measurement system 220 and to generallycontrol the operation of the meter 200, the meter 200 employs computerprocessing hardware (processor) 230 which executes programmedinstructions (on computer-readable media) according to a measurementalgorithm. Data processed by the processing system 230 is stored in aconventional memory device 235, e.g., non-volatile memory. Furthermore,the meter has a user interface 240 which includes a display 245.Pushbuttons, a scroll wheel, touch screens, or any combination thereof,are also provided as a part of the user interface 240 to allow a user tointeract with the meter 200. The display 245 typically shows informationregarding the testing procedure and/or information in response tosignals input by the user.

Diagnostic systems, such as blood-glucose testing systems, typicallycalculate the actual glucose value based on a measured output and theknown reactivity of the reagent-sensing element (e.g., test sensor 100)used to perform the test. Calibration information is generally used tocompensate for different characteristics of test sensors, which willvary on a batch-to-batch basis. The calibration information may be, forexample, the lot specific reagent calibration information for the testsensor. The calibration information may be in the form of a calibrationcode. Selected information associated with the test sensor (which mayvary on a batch-to-batch basis) is tested to determine the calibrationinformation to be used in association with the meter. The reactivity orlot-calibration information of the test sensor may be provided on acalibration circuit that is associated with the sensor package or thetest sensor. This calibration circuit may be inserted by the end user.In other cases, the calibration is automatically done using anauto-calibration circuit via a label on the sensor package or the testsensor. Embodiments of the present invention provide either a manual- orauto-calibrating diagnostic system. In the example shown in FIG. 1, thediagnostic system 10 is auto-calibrating, so the test sensor 100 mayinclude an auto-calibration information area 120, which may include alabel, at the meter-contact area 112.

Calibration of test sensors is required due to various factors. Thesefactors include reagent sample size and manufacturing tolerances of themeasurement system 220, such as electrode size, and separation dimensionbetween adjacent electrodes. However, the temperature of the reagent onthe test sensor 100 may also affect the accuracy of the concentration ofanalyte calculated by the meter 200, as the level of reaction betweenthe analyte and the reagent 115 may be dependent on the temperature ofthe reagent 115. Generally speaking, a reagent will react differentlywith two equal samples if the temperature of the reagent is not equal.As such, embodiments of the present invention determine a temperaturefor the reagent 115 and use this calculated temperature to produce amore accurate measurement of the analyte concentration. In particular,the meter 200 has a temperature-measuring system 250 and the processingsystem 230 uses this calculated temperature from thetemperature-measuring system 250 as a variable input for a measurementalgorithm. The operation of the temperature-measuring system 250 andother aspects of the test system 10 shown in FIGS. 1 and 2 are describedin U.S. patent application Ser. No. 12/252,348 titled “Method andAssembly for Determining the Temperature of a Test Sensor” and filed May2, 2009, the contents of which are incorporated entirely herein byreference.

In the embodiment illustrated by FIGS. 3A-E, the temperature-measuringsystem 250 includes a thermopile sensor 251 disposed at a positionwithin the test-sensor opening 210 on a printed circuit board 231. Asshown in FIG. 3E, the temperature-measuring system 250 is positioned inthe test-sensor opening 210 of the meter body 205, such that thetemperature-measuring system 250 is positioned in proximity to the testsensor 100 when it is inserted into the test-sensor opening (receivingport) 210.

Although some embodiments may include a temperature-measuring system 250disposed at a position within the test-sensor opening 210, atemperature-measuring system 250 may be disposed at other areas to allowtemperature measurement of test sensor 100. Moreover, other embodimentsmay include more than one structure disposed anywhere relative to themeter body 205 for measuring more than one area of the test sensor 100.Temperature measurements from more than one area may provide a moreaccurate determination of the temperature for the reagent 115.

In general, all materials at temperatures above absolute zerocontinuously emit energy. Infrared (IR) radiation is part of theelectromagnetic spectrum and occupies frequencies between visible lightand radio waves. The IR part of the spectrum spans wavelengths fromabout 0.7 micrometers to about 1000 micrometers. The wave band usuallyused for temperature measurement is from about 0.7 to about 20micrometers. The thermopile sensor 251 measures the actual sensor striptemperature by using IR radiation emitted from the test sensor 100. Byknowing the amount of IR energy emitted by the test sensor 100 and itsemissivity, the actual temperature of the test sensor 100 can bedetermined. In particular, the thermopile sensor 251 generates a voltageproportional to incident IR radiation. Because the temperature of asurface of the test sensor 251 is related to the incident IR radiation,the temperature of the surface can be determined from the thermopilesensor 251.

When the test sensor 100 is received into the test-sensor opening 210,the position of the thermopile sensor 251 is proximate, or substantiallyadjacent, to the test sensor 100. The position ensures that the IRradiation detected by the thermopile sensor 251 comes substantially fromthe test sensor 100. In other words, the thermopile sensor 251 ispositioned to minimize the effect of light from external sources, e.g.,ambient light, on the readings of the thermopile sensor 251. As shown inFIG. 3E, the thermopile sensor 251 includes a detecting surface 252 thatfaces the meter-contact area 112 and receives the IR radiation from thetest sensor 100 positioned in the meter 200. While FIG. 3E shows thethermopile sensor 251 below the test sensor 100, it is understood thatthe thermopile sensor 251 may be positioned in other appropriatepositions relative to the test sensor.

As shown in FIGS. 3F-G, the temperature-measuring system 250 includes areceiving port 253. The receiving port 253 is aligned with thetest-sensor opening 210, so that the receiving port 253 receives themeter-contact area 112 of the test sensor 100 when the test sensor 100is inserted into the test-sensor opening 210. The thermopile sensor 251is positioned relative to the receiving port 253 so that it can accessthe meter-contact area 112 for measurement when the test sensor 100 isreceived by the receiving port 253.

FIG. 3H illustrates aspects of a processing system 230 that are employedfor implementing the thermopile sensor 251 in the meter 200. First, anoutput electrical signal from the thermopile sensor 251 is received byan analog amplifier 230A. The amplified analog signal from the analogamplifier 230A is passed to an analog-to-digital converter 230C via ananalog filter 230B. The analog-to-digital converter 230C digitizes theamplified analog signal, which may subsequently be filtered by a digitalfilter 230D. The digital signal is then transmitted to a microcontroller230E. The microcontroller 230E calculates the temperature of the testsensor 100 based on the magnitude of the output electrical signal fromthe thermopile sensor 251 and the calculated temperature is employed tocorrect the initial blood glucose measurement from the measurementsystem 220. For some embodiments, it is contemplated that the analogfilter 230B, the analog-to-digital converter 230C, and the digitalfilter 230D may be incorporated into the microcontroller 230E. In someembodiments, the analog filter 230B and the analog-to-digital converter230C may be integrated into an application-specific integrated circuit(ASIC). In further embodiments, a memory, such as an EEPROM, may beemployed to store calibration data and the like. Moreover, it is furthercontemplated that in some embodiments the analog filter 230B and thedigital filter 230D may be optional. It is also noted that although thethermopile sensor 251 in FIG. 3E is positioned opposite from theelectrical contacts 221 that receive the test sensor electrodes, otherembodiments may position the thermopile sensor to be on the same side ofthe test sensor.

The use of a thermopile sensor to measure the temperature of the testsensor is further described in U.S. patent application Ser. No.12/252,348 titled “Method and Assembly for Determining the Temperatureof a Test Sensor” and filed May 2, 2009, the contents of which areincorporated entirely herein by reference. The accuracy of such systemsmay be further improved if aspects of the temperature-measuring systemare also calibrated. Thus, embodiments of the present invention provideimproved techniques for implementing and calibrating atemperature-measuring system to obtain more accurate and reliabletemperature measurements of the test sensor.

For example, embodiments may achieve further accuracy for temperaturemeasurements by employing a diagnostic system that detects the existenceof conditions that may affect accuracy. Tests have shown thatenvironmental conditions can have a significant effect on thetemperature measurement by a thermopile sensor. In particular,condensation, dust, and dirt on the detecting surface of the sensor maycause the thermopile sensor to read the temperature of an object, suchas a test sensor, incorrectly. To address such situations, thetemperature-measuring system 250 may include a reference object 254, asshown in FIGS. 3E and G. In general, the reference object 254 provides atechnique for testing the accuracy of the thermopile sensor 251. Thereference object 254 may be a structure originally designed as a part ofthe meter 200 or may be a structure that is specifically designed anddedicated for testing and calibration of the thermopile sensor 251.

As further illustrated in FIG. 3F, the temperature-measuring system 250may include a window, or aperture, 256. FIG. 3G shows the referenceobject 254 positioned at the window 256. The window 256 is aligned withthe detecting surface 252 of the thermopile sensor 251. The referenceobject 254 is positioned relative to the window 256, so that thethermopile sensor 251 is able to view the reference object 254 via thewindow 256 when a test sensor 100 is not positioned within receivingport 253. Because the reference object 254 is in the field-of-view (FOV)of the thermopile sensor 251, the thermopile sensor 251 can measure theIR radiation of reference object 254. In alternative embodiments, awindow 256 is not necessary to provide the thermopile sensor 251 with aview of the reference object 254.

The reference object 254 is controlled to reach a known, constanttemperature. As shown in FIG. 3G, the reference object 254 includes aresistor 255 that reaches a known, constant temperature when it receivesa current. When subject to the specified current, the resistor 255reaches a constant temperature each time and therefore emits the sameamount of IR radiation each time. The known, constant temperatureprovides a reference temperature by which the temperature-measuringsystem 250 may be tested and calibrated.

An approach for employing the reference object 254 is illustrated inFIG. 4. In acts 402 a-c, reference measurements may be taken from thethermopile sensor 251 during the manufacturing or assembly process. Inparticular, in act 402 a, a specified current is passed through theresistor 255 associated with the thermopile sensor 251. In act 402 b,the thermopile sensor 251 measures the IR radiation emitted from thereference object 254 in its FOV to obtain a temperature T_(O1) for thereference object 254. In act 402 c, the measurement T_(O1) is stored inmemory and is used as reference data for testing and calibration.

During operation, the assembled meter 200 periodically wakes up thethermopile sensor 251 according to a timing algorithm to perform adiagnostic test according to steps 404 a-d in FIG. 4. In act 404 a, thecurrent specified during manufacturing is passed through the resistor255 associated with the thermopile sensor 251 to achieve referencetemperature T_(O1). In act 404 b, the thermopile sensor 251 measures theIR radiation emitted from the reference object 254 in its FOV to obtaina test temperature T_(O2) for the reference object 254. Then, in act 404c, the test temperature T_(O2) is compared to the reference temperatureT_(O1) retrieved from the memory. In act 404 d, a signal is issuedindicating the results of the comparison. For example, if a metricrepresenting the difference between the test temperature T_(O2) and thereference temperature T_(O1) is greater than a predefined threshold, itis assumed that the thermopile sensor 251 is not functioning optimally,e.g., the detecting surface 252 of the thermopile sensor 251 is damagedor obstructed. In response, the thermopile sensor 251 may be furthercalibrated to adjust for the non-optimal operation of the thermopilesensor 251. For example, data for adjusting the measurements from thethermopile sensor 251 for a particular difference between T_(O1) andT_(O2) may be predetermined and also stored in the memory.

Alternatively, rather than measuring a known, constant temperature,other embodiments may measure the rate of heat change of the referenceobject 254 as the resistor 255 receives current. If the rate of heatchange measured by the thermopile sensor 251 does not substantiallymatch the expected rate of heat change (reference data), it is assumedthat the thermopile sensor 251 is not functioning optimally and thethermopile sensor 251 can be correspondingly calibrated.

To heat the reference object 254 to a known, constant temperature, otherembodiments may heat the body of the thermopile sensor 251, which isproximate to the reference object 254. Referring to FIG. 5, anotherdiagnostic test for the thermopile sensor 251 is illustrated. In acts502 a-c, reference measurements may be taken from the thermopile sensor251 during the manufacturing or assembly process. In particular, in step502 a, the thermopile sensor 251 measures the temperature T_(OA1) of thereference object 254 in its FOV while the body of the thermopile sensoris heated to a temperature T_(S1). Then, in act 502 b, the thermopilesensor 251 measures the temperature T_(OA2) of the reference object 254while the body of the thermopile sensor 251 is at a differenttemperature T_(S2). The body of the thermopile sensor 251 may be heatedby an internal or external active electrical circuit to achievetemperatures T_(S1) and T_(S2). For example, the circuit may include aheating element similar to the resistor 255 described previously. In act502 c, the measurements T_(OA1) and T_(OA2) are stored in memory and areused as reference data for testing and calibration.

During operation, the assembled meter 200 periodically wakes up thethermopile sensor 251 according to a timing algorithm to perform thediagnostic test according to steps 504 a-c in FIG. 5. In act 504 a, thethermopile sensor 251 measures the test temperature T_(OB1) of thereference object 254 in its field of view (FOV) while the body of thethermopile sensor 251 is at temperature T_(S1) specified during themanufacturing process at act 502 a. Then, in act 504 b, the thermopilesensor 251 measures the test temperature T_(OB2) of the reference object254 while the body of the thermopile sensor 251 is at a differenttemperature T_(S2) specified during the manufacturing process at act 502b. In act 504 c, the test temperatures T_(OB1) and T_(OB2) are comparedto the reference temperatures T_(OA1) and T_(OA2). In act 504 d, asignal is issued indicating the results of the comparison. For example,if a metric representing the differences between the test temperaturesT_(OB1) and T_(OB2) and the reference temperatures T_(OA1) and T_(OA2)is greater than a predefined threshold, an error signal is issued. Inthis case, it is assumed that the thermopile sensor 251 is notfunctioning optimally. If the thermopile sensor 251 is covered withdust, for example, the thermopile sensor 251 measures a test temperaturethat is higher than the reference temperature of the reference object,because the thermopile sensor 251 is also detecting the temperature ofthe dust. The dust is in contact with the body of the thermopile sensor251 and thus has a temperature closer to that of the body of thethermopile sensor and generally greater than that of the referenceobject, which is not in contact with the thermopile sensor. In response,the thermopile sensor 251 may be further calibrated to adjust for thenon-optimal operation of the thermopile sensor 251. For example, datafor adjusting the measurements from the thermopile sensor 251 fordifferences between the reference and test temperatures may bepredetermined and also stored in the memory. FIG. 5 illustrates thatmore than one reference temperature may be employed to test thetemperature-measuring system 250.

As an alternative, instead of employing a reference object that isintegrated or attached to the meter, the reference object may beprovided on a separate calibration device that is removably insertedinto the meter. For example, such a calibration device 300 isillustrated in FIG. 6. The calibration device 300 includes a heatingelement 310 and a flange 320. The flange 320, which extends from theheating element 310, may be similar in shape to a test sensor to permitinsertion into the test-sensor opening. As FIG. 6 illustrates, theflange 320 includes a reference object 354, which performs the samefunction as the reference object 254 described previously. The referenceobject 330 is coupled to the heating element 310, which may be poweredusing an internal power source, power from the meter, or an alternatepower source. Accordingly, at regular intervals or time periods, a usermay insert the calibration device 300 into the meter, which may also besimilar to the meter 200 described previously. Like a test sensor, theflange 320 is inserted into the test sensor opening of the meter andinto the receiving port of a temperature-measuring system. The referenceobject 354 is positioned proximate the thermopile sensor of thetemperature-measuring system, i.e., within the field-of-view of thethermopile sensor. As power is delivered to the heating element 310, thereference object 354 reaches a known, constant temperature orexperiences changes in temperature at a known rate. The IR radiationemitted from the reference object 354 is measured by thermopile sensor.If the measured quantity of IR radiation does not correspond to thetemperature characteristics of the reference object 354, it is assumedthat the thermopile sensor is not functioning optimally and thethermopile sensor is calibrated to adjust for the change infunctionality.

Although the embodiments described above may employ resistors as heatingelements, other types of heating elements may be employed according toaspects of the present invention. For example, an IR diode or IR LED maybe employed. Alternatively, a visible spectrum LED may be employed,where the LED is driven with relatively high current. The visiblespectrum LED may provide illumination of the test sensor opening whilealso providing a heating element for testing and calibrating thethermopile sensor. It is further understood that the heating elementsdescribed herein only represent an example of how the temperature of thereference object may be controlled. Alternatively, the temperature ofthe reference object may be controlled with a cooling element that coolsthe reference object to a reference temperature.

Furthermore, although embodiments described herein may employ thermopilesensors, which measure IR radiation to determine temperature, thetemperature-measuring system 250 of other embodiments employ anoptical-sensing system 262, as illustrated in FIG. 7. Rather thanmeasuring IR radiation, the temperature-measuring system 250 maydetermine temperature by measuring light reflected from a thermochromicmaterial. The use of thermochromic materials are described, for example,in U.S. patent application Ser. No. 12/252,348, titled “Method andAssembly for Determining the Temperature of a Test Sensor” and filed May2, 2009, the contents of which are incorporated entirely herein byreference. As shown in FIG. 7, the test sensor 110 includes athermochromic material 113, which indicates the temperature of the testsensor 110. The optical-sensing system 262 includes a light source 263and a light detector 264. The light source 263 directs photons at thethermochromic material 113 and the light detector 264 collects reflectedphotons to determine the temperature of the test sensor 110. Accordingto aspects of the present invention, a thermochromic material 266 mayalso be applied to a reference object 254, which is in the FOV of theoptical-sensing system 262. Although the reference object 254 in FIG. 7may be a part of the meter, it may also be provided on a removablyinsertable calibration device as shown in FIG. 6. The temperature of thereference object 254 may be controlled to achieve a referencetemperature as described previously, and the optical-sensing system 262is diagnostically tested by comparing the test temperature measured bythe optical-sensing system 262 and the reference temperature.

In general, the diagnostic test detects conditions, e.g., environmentalcontaminants or component failure, that cause a thermopile sensor tomeasure incorrect temperatures relative to reference calibrationmeasurements. Advantageously, implementing a diagnostic test asdescribed previously provides closed-loop control of temperaturemeasurement by a thermopile sensor and helps to maintain the integrityof the temperature measurement.

According to aspects of the present invention, the temperature-measuringsystem may be further calibrated to achieve more accurate temperaturemeasurements. In further embodiments, the temperature-measuring systemis calibrated to correct for offset and gain errors that occur inprocessing the signal. In particular, offset and gain errors may beassociated with any precision operational amplifiers that are used toamplify the signal of the thermopile sensor. In addition, thetemperature-measuring system may be calibrated to account for theconfiguration associated mechanical alignment of the thermopile sensoras well as the field-of-view, aperture size, etc.

Operational amplifiers may be interfaced with the thermopile sensor asseparate components during assembly of the meter, and calibration may beperformed after the meter has been completely assembled. For example,each assembly may be calibrated by exposing the active area of thethermopile sensor to a black body target. Complete assembly is generallyrequired before calibration, because the operational amplifiers whichare interfaced with the thermopile sensor can also contribute to gain,offset, and non-linearity errors that affect the temperature reading. Itis often difficult, however, to calibrate for the thermopile sensor andoperational amplifiers after the meter is completely assembled. Toachieve accurate calibration, the thermopile sensor must be exposed to aprecisely controlled target. More specifically, the surface radiationintensity of the target must be precisely controlled. The thermopilesensor is configured to measure the temperature of a test sensor uponassembly of the meter, and the geometry of the test sensorport/connector makes it very difficult to perform accurate calibrationand to meet regulatory standards, e.g., FDA standards.

Aspects of the present invention provide an improved technique forcalibrating the temperature-measuring system during assembly of themeter. Accordingly, as shown in FIG. 8, a meter employs a temperaturemeasurement module (e.g. chip package) 831. The temperature measurementmodule 831 includes a thermopile sensor 851 with a built-in ASIC 870which provides a preamplifier 872 for the thermopile sensor 851. In somecases, the interface to the temperature measurement module 831 issimplified, so that the interface with external circuits does notintroduce large error. Accordingly, all the components that makecalibration necessary, i.e., the thermopile sensor 851 and the ASICpreamplifier 872, are pre-assembled into the temperature measurementmodule 831.

The characteristics of the temperature measurement module 831 aredetermined, at least in part, by (1) the relative position between thethermopile sensor 851 and the aperture 856 through which the IRradiation is detected; and (2) the manner in which the thermopile sensor851 is connected to and paired with the ASIC 870.

As FIG. 8 further illustrates, the temperature measurement module 831also includes an integrated memory 880, which can store the calibrationdata. Thus, the temperature measurement module 831 includes all threenecessary electrical components for a functioning temperature-measuringsystem: (1) the thermopile sensor 851, (2) the ASIC pre-amplifier 872,and (3) the memory 880. The memory 880, for example, may be asemiconductor memory chip, such as an EEPROM, or a one-time programmable(OTP) memory. The memory 880 provides extra memory to store systemalgorithm constants. The information on the memory 880 may include, butis not limited to: sensor serial number, data format identifier,production lot identification, sensor characteristic profile, sensorcalibration, and checksum. In some cases, it is advantageous to make theinformation on the memory 880 readable only after the temperaturemeasurement module 831 has been assembled into the meter.

Incorporating the memory 880 in the temperature measurement module 831provides a high level of integration that makes it possible to calibratefor the thermopile sensor 851 and the ASIC preamplifier 872 and to storethe calibration data in the memory 880 before the temperaturemeasurement module 831 is installed in the meter. In other words, thetemperature measurement module 831, rather than the assembled meter, ismore easily calibrated with a blackbody and modeled, for example, to athird-order polynomial. In addition, all information relating totemperature measurement may be stored on the temperature measurementmodule 831. The temperature-measuring system 250 shown in FIGS. 4 and 5may be calibrated as a part of the temperature measurement module 831,and the reference temperatures may be stored in the memory 880. Thus,calibration can be completed at an early stage of the manufacturingprocess. Cost savings can be realized for the assembler of the meter,who is not required to perform any calibration after assembly.Furthermore, it is possible to integrate all the functional blocks ontoa single semiconductor chip to reduce the size of and the cost ofimplementing the temperature measurement module 831.

While various embodiments in accordance with the present invention havebeen shown and described, it is understood that the invention is notlimited thereto. The present invention may be changed, modified andfurther applied by those skilled in the art. Therefore, this inventionis not limited to the detail shown and described previously, but alsoincludes all such changes and modifications.

1-19. (canceled)
 20. A device for determining an analyte concentrationin a fluid sample, comprising: a receiving port configured to receive atest sensor, the test sensor including a fluid-receiving area forreceiving a fluid sample, the fluid-receiving area containing a reagentthat produces a measurable reaction with an analyte in the fluid sample,the test sensor having a test-sensor temperature; a measurement systemthat measures the reaction between the reagent and the analyte; atemperature-measuring system configured to measure the test-sensortemperature when the test sensor is received into the receiving port, aconcentration of the analyte in the fluid sample being determinedaccording to the measurement of the reaction and the measurement of thetest-sensor temperature; and a diagnostic system including a referenceobject that achieves a reference temperature, the temperature-measuringsystem being further configured to measure at least one test temperatureof the reference object, the diagnostic system being configured todetermine an accuracy of the temperature-measuring system based on theat least one test temperature measurement of the reference objectmeasured by the temperature-measuring system.
 21. The device of claim20, wherein the diagnostic system is configured to determine theaccuracy of the temperature-measuring system based on a comparisonbetween the at least one test temperature and a threshold value.
 22. Thedevice of claim 21, wherein the threshold value is the referencetemperature.
 23. The device of claim 20, wherein the at least one testtemperature includes a plurality of test temperatures and the diagnosticsystem determines a test rate of temperature change of the referenceobject based on the plurality of test temperatures, the diagnosticsystem being configured to determine the accuracy of thetemperature-measuring system by comparing the test rate of temperaturechange to an expected rate of temperature change for the referenceobject.
 24. The device of claim 20, wherein the receiving port, thetemperature-measuring system, and the diagnostic system are configuredto allow the temperature-measuring system to measure the test-sensortemperature when the test sensor is received in the receiving port andmeasure the at least one test temperature when the test sensor is notreceived in the receiving port.
 25. The device of claim 24, wherein thereceiving port includes a window and the temperature-measuring systemincludes a temperature sensor, the temperature sensor and the referenceobject being disposed on opposing sides of the window such that thetemperature sensor is configured to measure the at least one testtemperature of the reference object through the window when the testsensor is not received in the receiving port.
 26. The device of claim20, wherein the reference object is disposed on a calibration devicethat is removably inserted into the receiving port.
 27. The device ofclaim 20, wherein the reference object includes at least one of aresistor or a light emitting diode (LED).
 28. The device of claim 20,further comprising a cooling element configured to cool the referenceobject to the reference temperature.
 29. The device of claim 20, whereinthe temperature-measuring system includes a plurality oftemperature-measuring systems disposed at different locations within thedevice.
 30. A method for testing a meter, the meter determining ananalyte concentration in a fluid sample collected on a test sensor bymeasuring a reaction between the analyte and a reagent on the testsensor, the meter including a temperature-measuring system thatdetermines a test-sensor temperature, the meter using the test-sensortemperature as a parameter in determining the analyte concentration, themethod comprising: changing a temperature of a reference object to areference temperature, the reference object being positioned in themeter for measurement by the temperature-measuring system; determining,via the temperature-measuring system, at least one test temperature forthe reference object during or after the changing the temperature of thereference object; and determining an accuracy of thetemperature-measuring system based on the at least one test temperature.31. The method of claim 30, wherein the determining the accuracyincludes comparing the reference temperature to one or more of the atleast one test temperature determined after the reference objectachieves the reference temperature.
 32. The method of claim 30, whereinthe at least one test temperature includes a plurality of testtemperatures, the method further comprising determining a test rate oftemperature change of the reference object based on the plurality oftest temperatures, the accuracy of the temperature-measuring systembeing determined by comparing the test rate of temperature change to anexpected rate of temperature change for the reference object.
 33. Themethod of claim 30, further comprising calibrating thetemperature-measuring system based on determined accuracy of thetemperature-measuring system.
 34. The method of claim 33, wherein thecalibrating occurs at a time after the manufacture and assembly of themeter.
 35. The method of claim 33, wherein the determining the accuracyand the calibrating occur automatically on a periodic basis.
 36. Themethod of claim 33, wherein the calibrating includes correcting for oneor more offset or gain errors associated with a signal generated by atemperature sensor of the temperature-measuring system.
 37. The methodof claim 30, wherein the temperature-measuring system includes atemperature sensor, a pre-amplifier, and a memory as an integrated unitprior to installation of the temperature-measuring system into themeter.
 38. The method of claim 30, further comprising receiving acalibration device in a receiving port of the meter, the calibrationdevice including the reference object.
 39. The method of claim 30,wherein the reference object is integral with the meter adjacent to areceiving port, the test sensor being configured to be removablyinserted in the receiving port.
 40. The method of claim 30, wherein thechanging the temperature of the reference object includes heating atemperature sensor of the temperature-measuring system.